1. Field of the Invention
The present invention relates to a fitting structure for fastening a doctor blade provided in a developing device to regulate the amount of developer, a cleaning blade provided in a cleaning device, or the like in an image forming apparatus such as a facsimile machine, a printer, a copier, or the like, to the body of the apparatus.
2. Description of Related Art
In recent years, there have been very strong demands for higher image quality in image forming apparatuses. On the other hand, demands for lower costs have also been increasing. Thus, methods for reducing initial costs while maintaining high image quality have been sought. As one solution, attention has been paid to techniques for easy and accurate gap/contact width adjustment and fitting of a doctor blade in a developing device and of a cleaning blade in a cleaning device.
Ideally, such adjustment should best be dispensed with (adjustment-free); however, in adjustment of a dimension directly related to improvement of image quality, higher dimensional accuracy is demanded than common dimensional tolerances. For example, the gap of a doctor blade in a developing device has to be within a tolerance range as small as about ±0.05 mm to ±0.1 mm; otherwise, uneven density, fogginess, or carrier deposition may result.
The dimensions of, and the fitting accuracy of, a plate-form member such as a doctor blade or a cleaning blade have variations, and suppressing these variations further within common dimensional tolerances requires corresponding costs. Accordingly, when the plate-form member is fitted to the body of an apparatus, positioning adjustment is performed as one conceivable way of achieving tighter dimensional tolerances while suppressing increases in costs.
For example, Patent Document 1 (Japanese Patent Publication No. H07-181802) discloses a doctor gap adjustment mechanism which allows accurate automatic adjustment of the gap (doctor gap) between a developing roller and a doctor blade. Here, after temporary positioning is performed by use of temporary positioning pins, the doctor blade is offset by a predetermined amount by use of adjustment pins, and is thereby positioned.
On the other hand, according to Patent Document 2 (Japanese Patent Publication No. 2001-100517), a support portion is provided in a developing container, and when a doctor blade is fastened to the developing container, a backup member is brought into contact with the support portion to prevent deformation of the developing container. Patent Document 2 thus discloses a method of accurately positioning and fastening a doctor blade even when the doctor blade or another component has a manufacturing variation. Moreover, according to Patent Document 2, the edge position of the doctor blade is detected with a camera. Thus, even when the doctor blade sags in its thickness direction and thus has a variation, it is possible to suppress a variation due to screw tightening and achieve easy and accurate positioning. It is also possible to simplify the inspection process.
However, with the technology disclosed in Patent Document 1, the actual value of the doctor gap after adjustment is unknown, and therefore it needs to be checked in an inspection process as conventionally practiced. With the technology disclosed in Patent Document 2, consideration is given to the pressing force of a screw driver during screw tightening, but no consideration is given to the tightening torque that acts upon the doctor blade during screw tightening. Moreover, during screw tightening, the doctor blade is fastened with contact pins pressed against it; when the contact pins are pressed against it, the doctor blade may be displaced, or may yield to the screw tightening torque and slide.